Sites
Books

JavaScript Programmer's Reference JavaScript Programmer's Reference - This big book from Wrox press is a very good reference for JavaScript programming. Beginning Javascript Beginning Javascript - Another good book from Wrox press to start JavaScript programming. Definitely, not only for beginners.
Javascript : The Definitive Guide Javascript : The Definitive Guide - Despite of being such a fast changing language, this huge book (some odd 1000+ pages) manages to provide very useful and comprehensive guide for JavaScript, providing cross browser code in most cases. Online resources/documentations are the best ones for JavaScript, as they provide the latest information about the language which changes so fast and with all those cross browser compatibility issues.

News Groups

I believe, news groups prove very useful when you get stuck in a particular problem and need solution immediately, when you don't want to go through all those documentations to find what's missing, at times even though you have all the docs you just don't know what exactly applies to YOUR problem; news groups help you to find solution to your problem almost immediately with so many experts around the world voluntarily helping you with your specific problem.
Here are some JavaScript news groups -